Constant-current transformer.



No. 7l0,050. V Patented Sept. 30, I902, A. B. EVEREST.

CONSTANT CURRENT TRANSFORMER.

(Application filed Mar. 4', 1899.)

(N0 Model.)

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AUGUSTINE R. EVEREST, OF LYNN, MASSACHUSETTS, ASSIGNOR TO THE GENERALELECTRIC COMPANY, A CORPORATION OF NEW YORK.

CONSTANT-CURRENT TRANSFORMER.

SPECIFICATION forming part of Letters Patent No. 710,050, datedSeptember 30, 1902.

Application filed March I, 1899. Serial No. 707,721. (No model.)

To all whom, it may concern:

Beit known that I, AUGUSTINE R. EVEREST, a subject of the Queen of GreatBritain, residing at Lynn, county of Essex, State of Massachusetts, haveinvented certain new and useful Improvements in Constant- CurrentTransformers, (Case No. 1,021,) of which the following is aspecification.

My invention relates to alternating-current transformers for changingcurrents of constant potential to currents of constant volume or thereverse, and has reference more especially to that type of transformerin which relatively movable coils are employed. In some of its broaderaspects, however, my invention is not limited to use in connection withtransformers, but may be applied to a variety of electromagnetic deviceshaving relatively movable coils, motion between which is caused by theaction upon each other of currents flowing in the coils.

My invention is chiefly valuable,however, in connection withtransformers of the type above mentioned, and I use it in this relationfor the purpose ofobtaining betterregulation. Ihave observed that inconstant-currenttransformers such as already referred to the secondarycurrent at small loads, when the coils of the transformer are separatedfrom each other, is larger than at full load, when the coils of thetransformer areclose together. In these transformers, as is wellunderstood, the force of repulsion between the currents in the primaryand secondary coils is opposed by a suitablyapplied force the value ofwhich serves to determine the current at which the coils will separateor move apart from each other. WVith every decrease of load in thesecondary circuit there is a tendency toward increase of current and aconsequent increase in the force of repulsion between the primary andsecondary coils. The coils therefore move away from each other and moreleakage fiux is created between the coils than when in the originalposition. The secondary electromotive force is thus decreased, thustending to decrease the current to'its proper value. As above noted,however, I have observed that the load curve of the transformer is not astraight line, but shows a larger current at small loads than at fullload. In order to compensate for this defect, I provide a device-such,for example, asavariable counterweight-of such a nature as to decreasethe force urging the coils together the more the coils are separated.The decreased force of repulsion between the coils when they are widelyseparated is thus opposed by a correspondingly-decreased force urgingthe coils together. Under these conditions a given increase in secondarycurrent will produce an increased displacement of the coils andconsequent decrease in electromotive force sufficient to cut down thecurrent to its original value.

My invention will be more readily understood by reference to thefollowing description and accompanying drawing, while its scope will beclearly and particularly pointed out in the appended claims.

The drawing illustrates my invention as applied to analternating-current transformer.

The core of the transformer is here shown as of rectangular form, with amain core or bar 1 connected to end pieces secured within the castings 2and 3. Bars 1 and 5 are arranged parallel to the bar I, with their endslikewise secured in the end pieces in the castings 2 3. Clamping-bolts 6engage lugs 7 on corresponding ends of the end pieces 2 3 and serve toclamp the parts of the transformer together. Primary and secondary coilsare illustrated at 8 and 9, and both coils are arranged to embrace thebar 1 of the transformer-core. The coil 9 is preferably stationary andis arranged so as to rest on the lower cross-piece of thetransformer-core. The coil 8 is movable relatively to the coil 9 and issuspended from one end 12 of an oscillating lever by means of the loopedcord 10 and suspending-cord 11. So far as the principle of the inventionis concerned it is immaterial which of the coils 8 and 9 is the primaryand which the secondary.

The oscillatinglever 13 is mounted on knifeedges 14, carried by afork-shaped bracket 15, secured to the cross-bar or casting 2 of thetransformer-frame or otherwise suitably supported. The other end 16 ofthe oscillating lever carries a device similar in form to a cam, thesame being pivoted to the end of the A bolt 18, the head of which islever at 17.

Lil

not shown, passes through the end 16 of the oscillating lever andthrough a slot 19 in the cam 20, the slot being curved along arcs struckfrom radii with the bolt 17 as a center. By moving the cam so that theclamp ing-bolt 18 is secured in different positions in the slot 19 itwill be observed that the end 21 of the cam may be moved toward or awayfrom the fulcrum or axis of oscillation of the lever. The horizontalprojections of different points in the winding or cam surface 22 of thecam 20 are thus shifted relatively to the axis of oscillation of thelever 13. A cord 23 is connected to the winding-surface 22 at a pointindicated approximately at 24, and to the lower end of the cord a weight25 of suitable value is secured.

The cord 11, which carries the coil 8, engages a winding surface 26 ofcylindrical shape with its axis coincident with the axis of oscillationof the lever 13, to which the winding-surface is fixed. Whatever,therefore, be the position assumed by thelever the lever-arm supportingthe weight of the coil 8 remains the same. Such, however, is not thecase with respect to the lever-arm formed by the weight 25, draggingdownward upon the cord 23, passing over the winding-surface 22. Owing tothe eccentricity of this winding-surface the lever-arm or moment aboutthe axis of the lever is greater when the arm 16 is depressed than whenit is raised in the position illustrated.

The weight 25 is so chosen as partially, but not wholly, tocounterbalance the weight of the coil 8. Owing to the change in theleverarms above mentioned it will be seen that when the coils are closetogether the unbalanced weight of the coil 8 is greater than when thecoils are separated from each other.

' In describing the operation of myinvention it is unnecessary to setforth the mode of action of a constant-current transformer of the typeillustrated, since the same is well understood in the art. Concerningthe application of my improvement to this type of transformer, I maystate that the decrease in repulsion of the two coils when they areseparated from each other over that which takes place when they areclose together is probably due to the fact that the reluctance of themagnetic circuit for the leakage-lines of force which return througheach coil without threading through the other is greater when the coilsare separated than when they are close together. This increase inmagnetic reluctance is, however, small and varies with the particulartype of transformer employed. It will of course be obvious from what hasbeen said that the load curve of the transformer instead of being made astraight horizontal line may be given any other form by suitablychanging the law of the counterbalance. Whether or not this be thereason for the variation in the force of repulsion between the coils,the fact remains that such variation exists and thata device constructedas described for opposing to the force of re pulsion a force whichvaries with the load serves to bring the current in the secondarycircuit to the same value, whatever he the relative positions of thecoils, thus establishing the utility of my invention regardless of itstheory of operation.

Although unessential features of my invention, I may mention that atransformer of the type shown in the drawing is preferably inclosed inan iron casing, which may be filled with oil or other material forinsulating the parts of the transformer. With this arrangement thetransformer is generally. secured to the casing, such as illustrated at27, by means of brackets 28. The casing 27 is preferably formed ofsheet-iron and is riveted or otherwise secured to the cast base-plate29. A block of wood 30 rests on the top of the cast base-plate 29, and,if desired, may carry the weight of the transformer itself.

Having thus described my invention, what I claim as new, and desire tosecure by Letters Patent of the United States, is

1. The combination of relatively fixed and movable coils, one of whichis attached by suitable means to one end of an oscillating lever, adevice adjustably secured to the opposite end of the lever, and having acurved winding-surface, the centers of curvature of parts of which arenon-coincident with the axis of oscillation of the lever.

2. In an alternating-current transformer the combination of primary andsecondary coils, means for allowing the force of repulsion between thecurrents in the coils to cause a relative motion in a straight linebetween the coils, and means for opposing the force of repulsion by aforce which decreases as the load decreases.

3. In an alternating-current transformer the combination of primary andsecondary coils, means for allowing the force of repulsion between thecurrent in the coils to cause a relative motion in a straight linebetween the coils, and means for opposing the force of repulsion by aforce which is less at some given load than at a higher load.

4. In an alternating-current transformer the combination of primary andsecondary coils movable in a straight line relatively to each other, andmeans for opposing to the force of repulsion between the currents in thecoils, a force which varies in such a manner as to make the current inthe secondary coil at full load equal in value to the current in thesecondary coil when the load is small.

5. The combination of relatively fixed and movable coils, in mutualinductive relation to each other, an oscillating lever to one end ofwhich one of the coils is suitably attached, and a device with a curvedwinding-surface pivoted to the other end of the lever.

6. The combination of a core, a relatively movable coil cooperativelyrelated thereto, a pivoted member, means for supporting said coil fromsaid member, a device having an having a flexible connection passingover said Winding-surface.

9. The combination of a lever, a coil suspended from one end of thelever, means for applying a force of constant value to the other end ofthe lever, and means for automatically varying the point of applicationof said force to said lever.

In Witness whereof I have hereunto set my hand this 28th day ofFebruary, 1899.

AUGUSTINE R. EVEREST.

WVitnesses:

ALEX F. MACDONALD, DUGALD McKILLoP.

